The Cytogenetic Oncology Section has been examining specimens and tissue culture lines established from patients with hematologic malignancies and solid tumors in order to identify specific chromosomal changes associated with or diagnostic of these diseases. The breakpoints of these tumors indicate areas to look for new dominant oncogenes activated by translocatio while the areas of deletions and loss of material by non-reciprocal translocations highlight areas to search for recessive oncogenes. These cytogenetic studies provide additional evidence that multiple genetic lesio are associated with the development of malignant wars. We are investigating the contribution of inherited chromosome abnormalities and the susceptibili of peripheral lymphocytes to breakage (fragile sites) to the development of these diseases; lymphocytes of individuals with familial cutaneous malignan melanoma (CNM/dysplastic nevi syndrome (DN) and their spouses were studied. As part of the investigation of the etiology of the fragile sites, we are studying the relationship between topoisomerase I and II and the expression of fragile sites. In addition, the laboratory is conducting chromosomal in situ hybridization studies using either (3)H labeled probes or biotinylated probes to localize viral integration sites, and to localize other genes tha may be important to the development of malignant diseases.